Facsimile transmission mode signaling

Abstract

A facsimile transmitter comprises a rotatable drum and a detector for detecting dark-light variations in a document mounted on the drum. A frequency modulator is coupled to the detector for generating frequency modulated transmission signals representing dark-light variations in the document. A sync generator, which generates synchronizing pulses coincident with juxtaposition between the detector and the document-holding clamp on the drum, is also coupled to the frequency modulator. The transmission mode, e.g. the choice of utilizing an internal stable frequency or external power line frequency synchronizing signal to synchronize the drive of the drum, is signaled by varying the length of the synchronizing pulse during the sync period preceding transmission of document information.

What is claimed is: 
     
       1. A facsimile unit for transmitting signals representing dark-light variations in a document to a remote location comprising: detector means for detecting dark-light variations in a document;   scanning means for moving said detector means relative to the document;   first means for driving said scanning means at a rate directly proportional to and synchronized with the frequency of an internally generated signal in one transmission mode;   second means for driving said scanning means at a rare directly proportional to and synchronized with the frequency of an externally generated signal in another transmission mode;   mode signaling means for generating a signal representing the selection of said one or said other transmission mode; and   modulator means coupled to said detector means and said mode signaling means for generating modulated transmission signals representing dark-light variations in the document and the selected transmission mode.   
     
     
       2. The facsimile unit of claim 1 wherein said modulator means comprises means for generating frequency modulated signals representing dark-light variations in the document and the selected transmission mode, said modulator means generating signals of a first frequency representing a dark area on a document and signals of a second frequency representing a light area on a document. 
     
     
       3. The facsimile unit of claim 2 wherein said modulator means is responsive to said mode signaling means to repeatedly generate signals of a first frequency for a first duration followed by a second frequency of a second selected duration so as to represent the selected transmission mode prior to transmission of signals representing dark-light variations in the document. 
     
     
       4. The facsimile unit of claim 3 wherein said modulator means in response to said mode signaling means generates said signals of said first and second frequencies for said first and second predetermined durations repeatedly during a mode signaling period. 
     
     
       5. The facsimile unit of claim 4 comprising timer means for limiting the generation of said signals representing the selected mode to a predetermined period of time at the outset of a facsimile transmission period. 
     
     
       6. The facsimile unit of claim 4 wherein said mode signaling means comprises means for controlling said first duration with respect to said second duration at a substantially constant scanning rate, said first duration being increased relative to said second duration to indicate one mode selection and decreased relative to said second duration to indicate another mode selection. 
     
     
       7. The facsimile unit of claim 6 wherein said scanning means comprises a rotatably mounted drum, said detector means being juxtaposed to said rotatably mounted drum, said first and said second durations corresponding to predetermined angular positions of said drum. 
     
     
       8. The facsimile unit of claim 7 wherein said drum comprises clamp means for holding said document in place, said second frequency corresponds to a light region on a document and said second duration substantially coincides to juxtaposition between said detector means and said clamp means. 
     
     
       9. The facsimile unit of claim 8 wherein the generation of said first frequency for said first duration corresponding to the absence of juxtaposition between said detector means and said clamp means is discontinued after a predetermined mode signaling period. 
     
     
       10. The facsimile unit of claim 9 wherein the generation of said second frequency for a duration substantially coinciding with juxtaposition between said detector means and said clamp means continues after said mode signaling period so as to effectively blank out any shadows at said clamp means. 
     
     
       11. The facsimile unit of claim 1 in combination with another facsimile unit for receiving signals representing dark-light variations in a document, said other facsimile unit comprising: demodulator means for demodulating transmitted signals representing dark-light variations in a remotely located document;   transducer means juxtaposed to a copy medium for marking on the copy medium in response to demodulated signals representing dark-light variations in the remotely located document;   scanning means for moving said transducer means relative to the copy medium; and   mode signal detection means coupled to said demodulator means for automatically selecting the proper transmission mode.   
     
     
       12. The facsimile unit of claim 11 wherein said modulator means comprises means for generating frequency modulated signals representing dark-light variations in the document, said modulator means being responsive to said mode signaling means for generating signals of a first frequency representing a dark area on a document for a first predetermined duration between synchronizing signals followed by signals of a second frequency representing a light area on a document for a second predetermined duration during synchronizing signals. 
     
     
       13. The facsimile unit of claim 12 wherein said modulator means is repeatedly responsive to said mode signaling means so as to repeatedly generate said signals of said first and second frequencies of said first and second predetermined durations. 
     
     
       14. The facsimile unit of claim 13 wherein said scanning means comprises a rotatably mounted drum, said detector means being juxtaposed to said rotatably mounted drum, said first and second durations corresponding to predetermined angular rotations of said drum. 
     
     
       15. The facsimile unit of claim 14 wherein said drum comprises clamp means for holding said document in place, said second frequency corresponding to a light region on a document and said second duration corresponding to juxtaposition of said detector means with said clamp on said drum. 
     
     
       16. The facsimile unit of claim 15 further comprising timing means for terminating the generation of said second frequency for said second duration after a predetermined synchronizing period. 
     
     
       17. The facsimile unit of claim 1 wherein said mode signaling means comprises means for generating periodic signals of selected duration prior to transmission of video information representing dark-light variations during a synchronizing period, said periodic signals representing the predetermined relative position of said scanning means relative to said detector means, the time elapsed between said periodic signals being large relative to the duration of said periodic signals. 
     
     
       18. The facsimile unit of claim 17 wherein said scanning means comprises a rotatably mounted drum and said detector means is juxtaposed to said rotatably mounted drum, said periodic signals corresponding to predetermined angular positions of said drum. 
     
     
       19. The facsimile unit of claim 18 wherein said drum comprises clamp means for holding said document in place, said periodic signal being coupled to said modulator means so as to generate a modulated transmission signal resembling a transmission signal representing a light area. 
     
     
       20. The facsimile unit of claim 17 wherein said modulator means comprises means for generating frequency modulated signals representing dark-light variations in the document, said modulator means being responsive to said mode signaling means and said sync generator means for generating said first modulated synchronizing transmission signals characterized by a first frequency representing a dark area on a document for a first predetermined duration between synchronizing signals followed by said second modulated synchronizing transmission signals characterized by a second frequency representing a light area on a document for a second predetermined duration during synchronizing signals. 
     
     
       21. The facsimile unit of claim 20 wherein said modulator means is repeatedly responsive to said mode signaling means so as to repeatedly generate said signals of said first and said second frequencies for said first and said second predetermined durations. 
     
     
       22. The facsimile unit of claim 21 wherein said scanning means comprises a rotatably mounted drum, said detector means being juxtaposed to said rotatably mounted drum, said first and second durations corresponding to predetermined angular positions of said drum. 
     
     
       23. The facsimile unit of claim 22 wherein said drum comprises a clamp means for holding said document in place, said second duration corresponding to juxtaposition of said detector means with said clamp on said drum. 
     
     
       24. A facsimile unit for transmitting signals representing dark-light variations in a document to a remote location comprising: detector means for detecting dark-light variations in a document;   scanning means for moving said detector means relative to the document;   sync generator means coupled to said scanning means for generating synchronizing signals representing a predetermined relative position between said scanning means and said detector means;   modulator means coupled to said detector means and said sync generator means for generating modulated transmission signals representing dark-light variations in the document and said predetermined relative position between said scanning means and said detector means; and   mode signaling means associated with said sync generator means for selecting and controlling the duration of a plurality of said synchronizing signals in response to the selection of a transmission mode during an initial synchronizing period prior to transmission of video representing dark-light variations in a document, said mode signaling means operating by pulse width variation.   
     
     
       25. The facsimile unit of claim 24 wherein said mode signaling means comprises means for generating periodic signals of selected duration prior to transmission of video information representing dark-light variations during a synchronizing period, said periodic signals representing the predetermined relative position of said scanning means relative to said detector means, the time elapsed between said periodic signals being large relative to the duration of said periodic signals. 
     
     
       26. The facsimile unit of claim 25 wherein said scanning means comprises a rotatably mounted drum and said detector means is juxtaposed to said rotatably mounted drum, said periodic signals corresponding to predetermined angular positions of said drum. 
     
     
       27. The facsimile unit of claim 26 wherein said drum comprises clamp means for holding said document in place, said periodic signal being coupled to said modulator means so as to generate a modulated transmission signal resembling a transmission signal representing a light area. 
     
     
       28. A facsimile unit for transmitting signals representing dark-light variations in a document to a remote location: detector means for detecting dark-light variations in a document;   scanning means for moving said detector means relative to the document;   sync generator means coupled to said scanning means for generating synchronizing signals representing a predetermined relative position between said scanning means and said detector means;   frequency modulator means coupled to said detector means and said sync generator means for generating frequency modulated transmission signals representing dark-light variations in the document and said predetermined relative positions between said scanning means and said detector means;   first mode signaling means associated with said frequency modulator means for signaling the scanning rate of said scanning means, said first mode signaling means including means for varying the frequency of a transmission signal representing a light region on a document;   first drive means for driving said scanning means at a rate directly proportional to and synchronized with an internally generated drive signal;   second drive means for driving said scanning means at a rate directly proportional to and synchronized with an externally generated drive signal; and   second mode signaling means for signaling selection of the internally generated drive signal or the externally generated drive signal, said second mode signaling means including means for controlling the duration of the synchronizing signal and the duration of transmission signals representing the light region on a document during the synchronizing signal.   
     
     
       29. A facsimile unit for transmitting signals representing dark-light variations in a document to a remote location comprising: detector means for detecting dark-light variations in a document;   scanning means for moving said detector means relative to the document;   sync generator means coupled to said scanning means for generating synchronizing signals representing a predetermined relative position between said scanning means and said detector means;   modulator means coupled to said detector means for generating modulated video transmission signals representing dark-light variations, said modulator means also coupled to said sync generator means for generating a first modulated synchronizing transmission signal generally resembling a modulated video transmission signal corresponding to a dark area and a second modulated synchronizing transmission signal generally resembling a modulated video transmission signal corresponding to a light area; and   mode signaling means associated with said sync generator means and said modulator means for varying the duration of said second modulated synchronizing transmission signals in response to the selection of a transmission mode during a synchronizing period prior to the transmission of said modulated video transmission signals.   
     
     
       30. A facsimile unit for transmitting signals representing dark-light variations in a document to a remote location, of the type having a detector means for detecting dark-light variations in a document, scanning means comprising a rotatably mounted drum upon which said document is mounted by a clamp, a blanking generator means coupled to said scanning means for generating blanking signals representing a light condition of said document when said detector means is associated with said clamp, modulator means coupled to said detector means and to said blanking generator means for generating modulated transmission signals representing the dark-light variations in the document and wherein said blanking signals comprise a synchronizing signal representing a predetermined relative position between said scanning means and said detector means during an initial synchronizing period, wherein the improvement comprises: mode signaling means associated with said blanking generator means for varying the width of said blanking signal during the initial synchronizing period prior to transmission of video representing dark-light variations in said document.